Method and apparatus for reducing the temperature of pressurized liquids at near saturation temperature



July 26, 1966 R. A. FISHER 3,262,276

METHOD AND APPARATUS FOR REDUCING THE TEMPERATURE OF PRESSURIZED uqumsAI' NEAR SATURATION TEMPERATURE Filed July 8. 1964 FIGZ l2 l4 l6 I8 20INVENTOR.

ROBERT A. FISHER BY 471% W, I a MW .4 TTOR NE Y6 United States Patent3,262,276 METHOD AND APPARATUS FOR REDUCING THE TEMPERATURE OFPRESSURIZED LIQUIDS AT NEAR SATURATION TEMPERATURE Robert A. Fisher,Canoga Park, Califi, assignor to Martin- Marietta Corporation, New York,N.Y., a corporation of Maryland Filed July 8, 1964, Ser. No. 380,998 8Claims. (Cl. 62--5) This invention relates to an apparatus for reducingthe temperature of pressurized liquids, and more particularly to avortex evaporator sub-cooler used most advantageously in cooling liquidsof the cryogenic type.

Handling cryogenic liquids during missile loading operations iscomplicated by product-ion of vapor during transport, mass measurement,and tank loading. The liquid temperature in the storage tank is usuallyequal to or slightly above its normal boiling point. Heat transferred tothe pressurized liquid as it flows through lines and fittings adds tothe problem. The resultant vapor produced when the liquid isdepressurized upon entering the missile tank where the pressure is closeto the barometric value, may be prohibitive. Any vapor production in thetransport lines leads to excess friction effects through phaseinteraction. Additional release of vapor in the missile tank not onlyinterferes with the mass loading measurements but also limits the massof the cryogenic liquid which can be loaded. These effects may begreatly reduced by sub-cooling the liquid prior to tank entry.

The sub-cooling of cryogenic liquids may be effected by two methods;heat exchange with a substantially colder medium, and heat removal byevaporation.

The first method requires a heat exchanger with either liquid nitrogenor liquid helium as the heat transfer medium. The second method entailsreducing either the total pressure over the liquid or the partialpressure of the vapor in contact with the liquid. The partial pressuremay be reduced :by sweeping the ullage region of the tank with helium.While both of these methods are successful, they are subject to thedisadvantage of high cost and/ or cumbersome equipment. The secondmethod generally results in large losses of liquid. Also, helium is anatural resource which is subject to reserve limitations.

It is therefore, a primary object of this invention to provide means forsub-cooling pressurized liquids near saturation temperature which issimple, of relatively low cost, is completely passive in operation andhas a high rate of separation of gas from the sub-cooled liquid.

It is a further object of this invention to provide a device of thistype which automatically acts to re-pressurize the low temperature,high-pressure liquid after subcooling.

Further objects and advantages of this invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize this invention will be pointed out with particularity inthe following detailed description and claims and illustrated in theaccompanying drawing which discloses, by way of example, the principleof this invention and the best mode which has been contemplated ofapplying that principle.

In the drawing:

FIGURE 1 is a side elevational view, partially in section of oneembodiment of the vortex evaporative subcooler.

FIGURE 2 is a vertical sectional view of the device shown in FIGURE 1taken along lines 2-2.

FIGURE 3 is a reverse side elevational view of the device shown inFIGURE 1 with the outer plate re moved showing the fluid dischargearrangement.

FIGURE 4 is an exploded, perspective view of the elements forming theassembly shown in FIGURES 1 through 3 inclusive.

FIGURE 5 is a semi-schematic view similar to FIG- URE 2 of the deviceshown in FIGURES 1 through 4 inclusive, illustrating the principles ofoperation of the vortex evaporative sub-cooler.

In general, the present invention is directed to a method of loweringthe temperature of a body of pressurized liquid at near saturationtemperature comprising the steps of reducing the pressure of said liquidbody, moving said body in a circular path to evaporate a portion of thesuperheated liquid body adjacent the inner surface of said moving bodywhereby the temperature of the remaining portion of said moving liquidbody is reduced, and repressurizing said remaining liquid body atreduced velocity.

The apparatus of this invention comprises a completely passive vortexevaporator sub-cooler for reducing the temperature of cryogenic liquidsand the like and includes a circular vortex chamber with an inlet nozzlepositioned tangentially of and opening into said chamber. Means areprovided for directing high pressure liquid at near saturationtemperature through said nozzle for tangential delivery within saidchamber against the annular chamber wall to form a moving liquid annulusin contact with said chamber Wall and a vapor core centrally thereof. Adiffuser outlet is positioned tangentially of the circular chamberspaced axially of said inlet nozzle, in position to receive the highvelocity fluid for discharge therefrom at increased pressure and lowvelocity. At least one opening is formed co-axially of the circularchamber within the region occupied by the vapor core whereby vaporevaporated from the surface of the high velocity cryogenic liquid may befreely vented from the chamber while the liquid body is sub-cooledthereby.

Referring to the drawing, there is shown in FIGURES 1 through 4inclusive, a preferred embodiment of the completely passive, vortexevaporator sub-cooler for cooling cryogenic liquids and the like. Theassembly 10 forming a housing or cell consists of a series of plates 12,14, 16, 18, and 20, which are held together in sealed, abuttingrelationship. A series of through bolts indicated at 22 pass throughrespective bores 24 of each of the plates, the bores being aligned andsuitably spaced to produce a permanently sealed assembly regardless ofthe high pressure of the fluids passing through the vortex evaporatorsub-cooler. The three inner plates 14, 16 and 18 act to form an annularvortex chamber indicated at 26 in FIG. 2. It is important to note thatthe annular opening 28 formed within plate 18 is of lesser diameter thanthe annular opening 30 formed within plate 14, with both of theseopenings being larger in diameter than opening 32 formed within thecentral baffle plate 16. Reference to FIGURE 1 shows plate 18 having atapered inlet nozzle 34 in the form of a tapered duct of rectangularcross sectional configuration having an opening 36 tangent to theannular opening 28. A small section or rim of the plate 16 acts as aliquid baflle as can be seen in FIGURE 1. The pressurized liquid isdelivered to the assembly through conventional high pressure fluid inletcoupling member 38 which includes a threaded connector portion 40 forattachment to an inlet conduit (not shown), thereby receiving highpressure fluid as indicated by the arrow in FIGURE 1. Since the duct 34is tapered, high pressure liquid entering the duct 34 has its pressurehead transformed to velocity head. Therefore, the pressurized fluiddischarging from inlet nozzle 34 tangentially to the annular opening 28moves at high velocity about the surface wall formed by opening 28within the plate member 18 in an annular path. The liquid is charged asa thin stream which, as a result of centrifugal force, hugs the wall 28and rotates at high velocity. It tends to move over the lip or rim ofplate 16 into the portion of chamber 26 formed by the much largerdiameter opening 30.

The vortex evaporator sub-cooler is basically a refrigeration devicewhich produces a vortex of superheated liquid in an enclosed cell orchamber in much the same manner as the cyclone separator. The liquidwhich is near saturation temperature is effectively superheated by thelow pressure existing in the vortex and boils thus producing a vapor. Asa result of centrifugal force, the high artificial gravity field of thevortex readily separates this vapor from the liquid phase. The liquid isinjected tangentially to the chamber wall opening 28, through therelatively high velocity nozzle 34. As the velocity increases in thenozzle 34, the pressure decreases, creating a super heated condition inthe liquid and inducing boiling. The process continues into the vortexchamber 26 where the two phases are separated as a result of centrifugalforce acting upon the phases of different density. The evolved vapormoves outwardly from the chamber walls leaving a liquid annulus or bodywhich hugs the wall and a co-axial vapor core within the liquid annulus.As a result of evaporation, the liquid annulus hugging the chamber wallhas its temperature reduced and is therefore sub-cooled prior todischarge through the diffuser outlet best seen in FIGURE 3. FIGURE 3shows the larger diameter opening 30, eccentrically positioned, whichterminates in a rearwardly directed diffuser outlet 42. Appropriatefluid connection is made through an outlet coupling 44 similar tocoupling 38, including a threaded connecting means 46. The coupling 38may be connected to a fluid discharge conduit (not shown). The dischargeis shown by the lower arrow of FIGURE 3. The middle or central plate 16acts as a barrier or baffle allowing a thin film of high velocity liquidwhich is moving in a circular path about wall 28 to move over the lip ofopening 32 into the larger diameter opening 30 for discharge throughdiffuser outlet 42. The high velocity, low pressure fluid is convertedinto high pressure, low velocity fluid as a result of movement throughdiffuser 42 for discharge from the vortex-evaporator-cooler at reducedtemperature.

During movement of the high velocity fluid through the vortex chamber26, the induced boiling produces vapor which evolves from the surface ofthe liquid body. The evolved vapor is vented to the atmosphere throughvents co-axial to the circular vortex chamber 26. The outer plates 12and 20 carry, respectively, vent pipes 48 and 50 which extend throughopenings 54 within the respective plates 12 and 20, the vent pipeshaving their inner ends positioned within the vortex chamber 26. Tofacilitate mountnig of the pipes on respective plates 12 and 20, annularmembers 52 are welded to the pipes 48 or 50 and extend perpendicularthereto and are fixed to the outer surface of the respective plates 12and 20 in sealed relation thereto.

The principles utilized by the vortex cell asserts that a liquidelement, at saturation temperature and migrating toward a free surfacethrough a negative pressure gradient, evolves vapor. This assumes thatheat transfer by conduction and radiation between the liquid element andits environment is incapable of maintaining an unsaturated condition inthe element.

The ability of the unit to separate the vapor from the boiling liquid islimited by (l) the viscosity of the twophase mixture, (2.) the effect ofgravity field, and (3) the liquid surface area through which theescaping vapor must pass. Viscosity of the mixture is a function of theliquid-vapor mixture ratio, the temperature, and pressure. In the freevortex produced by the cell, the artificial gravity field due tocentrifugal force decreases with increasing distance from the center ofrotation. Since faster separation of the two phases occurs in a highergravity field, .a small gaseous core produces the best separatingconditions. However, the surface of the interface between the boilingliquid annulus and the vapor core, through which the generated vapormust pass, increases with increasing core diameter. The most efficientoverall system, therefore, is a compromise between these two features.

An experimental vortex evaporator sub-cooler which operatessatisfactorily includes a vortex unit having a chamber 2" in diameterand 1%" long. The injector head of the nozzle is in width by /2 inlength and the vent ports are /8 in diameter. Reference to FIG- URE 5shows a cross section of the device and its method of operation. Theliquid is introduced into inlet nozzle 34 of the cell 10 forming aliquid annulus 60 which hugs the inner wall opening 30' adjacent theinlet end of the chamber 26. The liquid annulus 60 moving at highvelocity and at reduced pressure allows superheated liquid to boil asindicated by the bubbles 62 adjacent the gaseous core, producing a netcooling effect on the remaining liquid body. The evolved vapor is ventedto the atmosphere through the vapor vents 48' and 50'. The test unitindicates that separation of vapor from the boiling liquid annulus israpid enough to allow high cool ing rates without experiencingappreciable losses of the residual liquid passing through diffuseroutlet 42' after passing over the baflle formed by opening 32'. In adevice of this type, a loss of approximately 7% of the liquid throughthe vents is considered appreciable.

It is to be noted that most of the boiling occurs just prior to andafter the pressurized fluid is injected into the vortex chamber from theinlet nozzle and that most of the boiling occurs at the interfaceexisting between the liquid phase, that is, annulus '60, and the gaseousphase or core located centrally thereof.

An analysis of the device of the size indicated operating on waterflowing at 0.4 pound per second in superheated 13 F., in a unit 2" indiameter and 1%" long provided a temperature drop as high as 6 F. as setforth later.

Several tests were made using water as the fluid near its saturationtemperature. The following table shows the results of 27 runs with thevarious columns indicating the flow rate of liquid in gallons perminute, the vent loss of liquid in percentage of total flow, the inlettemperature of the saturated water in degrees Fahrenheit, the outlettemperature of the sub'cool water and the temperature drops in degreesFahrenheit.

Vent Flow Loss, Inlet Outlet Run Rate, Percent Temp, Temp., 'I., F.

g.p.m. of Total F. F.

Flow

To prove that the cooling effect measured was due to boiling heattransfer only, the vent ports were periodically closed to stop theboiling process. The outlet temperature was observed to return to thevalue of the inlet temperature except for very high temperature runs.For these runs, the temperature was slightly less than the inlettemperature, one or two degrees Fahrenheit, and equal to the saturationtemperature at the pressure in the volute. The temperature apparentlydeveloped a super-heated condition in the water and boiled as thepressure decreased in the cell due to frictional losses.

The present invention has great application to cryogenic liquids becauseof the need in the missile industry to reduce the temperature of aliquid from its boiling by only a few degrees. The proposed methodrepressurizes the cool liquid and disposes of the vapor in a compactsystem as contrasted to the prior art methods which retain the gas inthe stream or if the gas is vented, the stream must be repressurized. Inthe present system initial pressure energy is converted to kineticenergy, most of which may be recovered as pressure after evaporation hasoccurred. Furthermore, the separation of vapor from liquid may takeplace at high rates in a confined space because the effects of densitydifference are magnified by centrifugal action.

Variations may occur in vortex cylinder diameter, height, bafiling,vapor venting and stream introduction and removal. These variations maytake the form of changes in size, shape and location of the componentsWithout departing from the spirit of this invention. For instance, thevortex chamber may include a series of annular sections separated byannular bafiies having openings of less diameter thereby insuring thatall of the high velocity fluid emanating from the nozzles reaches theportion of the liquid phase annulus adjacent the interface to allowboiling of the superheated portion of the liquid to inherently cool theremaining liquid body. Further, while the invention in a preferred formis shown as an assembly formed of a series of stacked plates, the unitmay be formed as a single casing or housing in integral form assuggested by the schematic teaching of FIGURE 5. It is to be noted thatthe present invention provides an extremely simple evaporation methodfor cooling pressurized cryogenic liquid and the like. A free vortex ofliquid is used to convert the pressure head to velocity head and, afterevaporation of some liquid, to reconvert velocity head to pressure head.The system operates on a steady flow basis. The process is accomplishedcontinuously without the use of moving parts by the method including thesteps of decompression, evaporation and recompression of the liquid. Theprocess is confined to a cylinder and its inlet and exit sections and iscarried on wholly within a single unit assembly.

While there has been shown and described and pointed out the fundamentalnovel features of the invention as applied to a preferred embodiment andmethod of operation, it will be understood that various omissions andsubstitutions and changes in the form and detail of the deviceillustrated and its method of operation may be made by those skilled inthe art without departing from the spirit of the invention. It is theintention, therefore, to be limited only as indicated by the scope ofthe following claims.

What is claimed is:

1. A method of temperature reduction of a body of pressurized liquid atnear saturation temperature comprising the steps of: depressurizing saidliquid body to cause superheating thereof, moving said liquid body in avortex path, evaporating a portion of the superheated moving liquid bodyin said vortex path whereby the temperature of the remaining portion ofsaid moving liquid body is inherently reduced, and repressurizing saidremaining liquid body.

2. A method of temperature reduction of a body of pressurized liquid atnear saturation temperature comprising the steps of: depressurizing saidliquid body to cause superheating thereof, whirling said depressurizedliquid body to form a vortex, evaporating a portion of the superheatedwhirling liquid body whereby the temperature of the remaining portion ofsaid liquid body is inherently reduced, and repressurizing saidremaining liquid body.

3. The method of lowering the temperature of a body of pressurizedliquid at near saturation temperature, comprising the steps of: reducingthe pressure of said liquid by changing pressure head to velocity headto cause superheating of said liquid body causing said depressurizedbody of liquid to move in a vortex path to allow a portion of thesuperheated moving liquid body to evaporate therefrom and to inherentlycool the remaining portion of said moving liquid body, and directing theremaining portion of said liquid body from said vortex path into adiffusing area to effect repressurization at reduced velocity.

4. The method of lowering the temperature of a body of pressurizedliquid at near saturation temperature comprising the steps of:depressurizing said pressurized liquid body to cause superheatingthereof, causing said depressurized liquid body to move in a vortex pathwhereby, as a result of centrifugal action, a portion of the superheatedliquid body evaporates therefrom to inherently cool the remainingportion of said moving depressurized liquid body, removing the vaporproduced by evaporation centrally of said vortex path and repressurizingthe remaining liquid body at reduced velocity.

5. A completely passive, vortex evaporator sub-cooler for pressurizedliquids at near saturation temperature comprising: a circular vortexchamber including first and second annular openings separated by abaflie having a circular opening of less diameter than said otheropenings, an inlet nozzle positioned tangentially to and opening intosaid first opening, means for directing said liquid through said nozzlefor tangential delivery within said chamber to form a moving annulus ofliquid in contact with said chamber wall and a vapor core centrallythereof, diffuser means positioned tangentially of said second openingspaced circumferentially from said first opening, in position to receivethe high velocity fluid for discharge therefrom at increased pressureand reduced velocity, and at least one vapor vent formed coaxially ofsaid vortex chamber within the region occupied by the vapor core wherebyvapor evaporated from the surface of said high velocity liquid may befreely vented from said chamber while said remaining liquid issub-cooled thereby.

6. A completely passive, vortex evaporator sub'cooler for lowering thetemperature of a body of pressurized liquid at near saturationtemperature, comprising a circular vortex chamber, an inlet nozzlepositioned tangentially to and opening into said chamber, means fordirecting high pressure liquid through said nozzle to form a movingliquid annulus in contact with said chamber wall and a vapor corecentrally thereof, a diffuser outlet positioned tangentially of saidcircular chamber, spaced circumferent-ially in said circular chamberfrom said inlet nozzle, and in position to receive the high velocityfluid for discharge therefrom at increased pressure and reducedvelocity, and at least one vapor vent in fluid communication with saidvapor core whereby vapor evaporated from the surface of said highvelocity liquid annulus may be freely vented from said chamber whilesaid remaining liquid body is sub-cooled thereby.

7. The apparatus as claimed in claim 6 further including an annularbafile member positioned centrally of said vortex chamber, between saidinlet nozzle and said diffuser outlet and having an opening of lessdiameter than the diameter of the remaining portions of said circularvortex chamber whereby said moving body of liquid passes over saidbaffle from said inlet nozzle to said diffuser outlet to enhanceseparation of vapor from the superheated liquid.

8. A completely passive, vortex evaporator sub-cooler for lowering thetemperature of a body of pressurized liquid at near saturationtemperature, said apparatus com- 'bly including a first central platehaving a first circular opening therein, a second plate positioned onone side thereof having an opening of slightly greater diameter, coaxialto said first opening, an inlet nozzle formed in said second platetangential to, and tapering inwardly toward, said second opening, athird plate positioned on the opposite side of said first plate fromsaid second plate having a third opening of a diameter larger than theopening of said second plate and positioned eccentrically with respectto said first and second openings, said third plate including a diffuseroutlet extending away from said third opening tangential with respectthereto and spaced circumferentially with respect to said inlet nozzle,said assembly further including a pair of end plates, vents formed inrespective end plates, means for directing said pressurized liquidthrough said inlet nozzle, and means for receiving repressurized liquidfrom said diffuser outlet, whereby gas evolved from the free surface ofsaid high velocity liquid moving within the free vortex passes outwardthrough said vents, and means for clamping said plates together to forma sealed assembly.

References Cited by the Examiner UNITED STATES PATENTS 2,893,216 7/1959Seefeldt 625 3,044,270 7/1962 Biever 62-55 3,129,075 4/1964 Anliot 6253,160,490 12/1964 Fabre 62-5 WILLIAM J. WYE, Primary Examiner.

1. A METHOD OF TEMPERATURE REDUCTION OF A BODY OF PRESSURIZED LIQUID AT NEAR SATURATION TEMPERATURLE COMPRISING THE STEPS OF: DEPRESSURIZING SAID LIQUID BODY TO CAUSE SUPERHEATING THEREOF, MOVING SAID LIQUID BODY IN A VORTEX PATH, EVAPORATING A PORTION OF THE SUPERHEATED MOVING LIQUID BODY IN SAID VORTEX PATH WHEREBY THE TEMPERATURE OF THE REMAINING PORTION OF SAID MOVING LIQUID BODY IS INHERENTLY REDUCED, AND REPRESSURIZING SAID REMAINTAINING LIQUID BODY. 